Vapor power plant with novel auxiliary flame igniter



F. COWAN ET AL VAPOR POWER PLANT WITH NOVEL AUXILIARY FLAME IGNITER IFiled Feb. 26, 1954 April 1, 1958 Frederick Cowun Joseph A. LocerenznHarvey C. Miflendorf flT'I'O Y5) w QM. V Q m E N 5 a I H w L 6 mm mm wnw t E mm mm vm E Y vw 8 N% W. Db M. wm mm I w mm w 9v 1 vm mm I Q N m mv .5 it E. U 4% l m vb u \\\\\.\\\-\\\\\\\Q n m9 mm mm Q mm e9 mm nitedState VAPOR POWER PLANT WITH NOVEL AUXILIARY FLAME IGNITER ApplicationFebruary 26, 1954, Serial No. 412,769

Claims. (Cl. 290-2) This invention relates to power plants employingvapor generators fired with a suitable fuel and methods of operatingsuch power plants and has particular relation to such a power plant andmethod wherein insurance is provided against an unstable flame conditionin the generator thereby eliminating the dangers and disadvantages whichaccompany such a condition.

in the operation of present day large steam generators, it is thepractice to use an auxiliary flame igniter to initially ignite the fuelsupplied to the furnaces of these generators through the rather largemain burners. Once this fuel has been lit these igniters areextinguished with the combustion of the fuel than being self-sustaining.The supply of fuel is controlled in accordance with the demand placedupon the power plant and as this demand decreases the rate of firing islikewise decreased. It has been found that when this firing rate isdecreased to a predetermined value or point the resulting flame in thefurnace begins to surge and becomes unstable resulting in poorcombustion efficiency and establishing a potentially extremely dangerouscondition since such an unstable flame may be extinguished completelycausing the furnace to fill with unburned fuel which if ignited willresult in an explosion.

With the present invention this inefficient and potentially dangerouscondition is eliminated by lighting the auxiliary flame igniter beforethe rate of fuel flow is decreased to the point where an unstable flameis produced with these igniters when activated having the effect ofstabilizing this flame throughout the entire lower end of the firingrange of the burners. The igniters are activated and deactivated by acontrol system which is effectively responsive to the load on the powerplant and this control system is arranged to automatically activate theigniters prior to the rate of firing of the boiler reaching the pointwhere the flame becomes unstable.

-t is an object of this invention to provide an improved power plantemploying vapor generators fired with suitable fuel and an improvedmethod of operating the same wherein unstable flame conditions in thegenerator are eliminated.

Other and further objects of the invention will become apparent to thoseskilled in the art as the description proceeds.

With the aforementioned objects in View, the invention comprises anarrangement, construction and combination of the elements of the powerplant in such a manner as to attain the results desired as hereinaftermore particularly set forth in the following detailed description of anillustrative embodiment, said embodiment being shown by the accompanyingdrawings wherein:

Figure 1 is a diagrammatic view of a power plant having a pulverizedcoal fired steam generator and embodying the igniter control system ofthe present invention;

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Figures 2, 3 and 4 show various detailed modifications I of the ignitercontrol system.

While the present invention is shown and described in connection with apulverized fuel fired installation it is to be understood that it isequally applicable Where other fuels are employed which produce anunstable flame at the low end of the range of the burner as for examplegas or oil.

Referring now to the drawing wherein like reference characters are usedthroughout to designate like elements the power plant diagrammaticallyillustrated in Figure 1 comprises a steam generator 10 having a furnace12 which is lined with steam generating tubes 14 and which is firs-dthrough a suitable burner 16. The steam and water mixture in tubes 14 isconveyed from the upper end thereof into steam and water drum 38 withthe water being conveyed from this drum through downcorner 2t? tocirculating pump 22 which pumps it into orifice drum 24 from which it isdistributed to tubes 14. Steam is conveyed from the top of drum 18through superheater 26 to turbine throttle valve 28 with the steam thatis delivered to this valve being maintained at a predetermined constanttemperature and pressure through suitable control means forming a partof the steam generator.

The fuel system for supplying burner 16 with pulverized fuel, such ascoal, includes pulverizing mill 3% connected to burner 16 by duct 32 anddriven by electric motor 34. Control of the rate of raw fuel deliveredto mill 36 is maintained by feeder 36 located at the bottom of storagehopper 38 and connected to the mill by duct 34?. This feeder may be ofany well known type and is operative to adjustably regulate the rate offeed from hopper 38 to mill 30. As diagrammatically illustrated thisrate of feed is adjusted by lever 2 with the rate being decreased as thelever moves in a clockwise direction as indicated by arrow 44.

The pressure of the steam delivered to throttle valve 2% is maintainedconstant or substantially constant by regulating the rate of fuel firedto furnace 12 and for so regulating this fuel firing, control mechanism46 is subjected to this steam pressure through conduit 48 and iseffective to regulate the operation of motor 51 to adjust lever 42 tothe desired setting, resulting in a fuel delivery rate which willproduce the desired steam pressure. Thus, as the steam pressure deviatesfrom the desired value lever 42 will be adjusted to correct the rate ofthe fuel supply to bring the pressure back to its desired value.

The amperage drawn by motor 34 varies in accordance with the rate offuel supplied to mill 30 with this amperage increasing as the rate offuel supplied is increased.

Adjacent the burner 16 is auxiliary flame igniter 50 which is suppliedwith fuel (preferably oil) and air through conduits 52 and 54respectively, and which, as diagrammatically disclosed, is provided withan electric spark igniter element 56. The flow through conduits 52 and54 is controlled by valves 58 and en respectively, these valves beingnormally biased closed and being opened by electromagnet 62 uponenergization of this electromagnet. The electric circuit for thiselectromagnet, designated generally 63, comprises a pair of conductors64 and 66 connected across a potential 68. The electric spark igniterelement 56 is electrically connected into this circuit in parallel withelectromagnet 62 so that upon energization of the circuit valves 53 and6h will be moved to an open position simultaneously with theenergization of igniting element 56 thereby resulting in activation ofauxiliary flame igniter 50. The flame igniter 50 is so positionedrelative to burner 16 that when the flame igniter is activated the flameit produces extends into the mass of fuel which burner 16 projects intothe furnace.

As embodied in the Fig. 1 organization, in series with conductor 64 isthe manual control switch 70 for effecting manual control of flameigniter 563 as desired. Also in series with this conductor are thecontacts of relay 72 which are biased to the closed position by spring7d. Energization of coil '76 of this relay 72 is controlled bytransformer '78 which has its primary winding in the circuit of motor 34and its secondary winding in the circuit of the coil. Thus, as theamperage drawn by motor 3d increases the current flow through the coilwill likewise increase thereby increasing the magnetic attractionproduced by this coil so that at a prede :rmined current flow themagnetic force created by the coil will be sufficient to overcome thebias of spring 74 causing the contacts of the relay to open while forall current flows below this predetermined value the bias of spring Mwill be greater than this mag etic force and the contacts of the relaywill remain closed. By adjusting the tension of spring 7 or the relationbetween the primary and secondary coils of transformer 78 the amperagedrawn by motor 34 which is effective to actuate relay '72 may beselected as desired.

In order that auxiliary flame igniter .ill will be activated and inoperation before the rate of fuel supply through burner 16 becomes solow that an unstable flame is produced the operation of relay '72 isregulated so that the contacts of the relay will close when the rate offuel supply to mill 30 reaches a predetermined value which is above thatwhich will result in an unstable flame, this predetermined value beingevidenced by a predetermined current flow through the circuit of motor34. Thus when the rate of fuel supplied to mill 3i) decreases to thispredetermined value the contacts of relay 72 will close resulting inenergization of electromagnet 62 and igniting element 56 and consequentactivation of auxiliary flame igniter 50. With this rate of fuel supplythe flame is still stable, but as the rate is further decreased theflame would ordinarily become unstable if flame igniter 56 were not inoperation. However, with flame igniter 50 in operation the rate of fuelsupplied may be lowered to the lowest range of the burner with the flameremaining stable and there being no danger of it being extinguished andcausing an explosion.

The superheated steam produced by superheater 26 is supplied throughthrottle valve 28 to turbine 80 with the exhaust from this turbine beingcondensed and returned to the steam generator in a well known andconventional manner. The turbine 88 is connected with and drives theelectric generator 82 which supplies electric energy to a variable loadthrough transmission lines 84 with this variable load being what isknown as the load on the power plant or the load supplied or met by thepower plant. Since the frequency of the alternating current produced bygenerator 82 must be maintained constant the generator must be driven ata constant rotational speed as for example 1800 R. P. M. For thispurpose the speed of the turbine and accordingly the speed of thegenerator is controlled by a suitable governor connected with valve 28and operative to regulate this valve to control the steam flow toturbine 80 to maintain the speed of the turbine constant. While thereare numerous conventional governing mechanisms for accomplishing thiscontrol, for the purposes of illustration, there is shown in the drawingthe well known fly ball type of governor which includes pivoted arms 36connected with vertically movable sleeve 88 and effective to move thesleeve up and down as the turbine speed increases or decreasesrespectively. The operating stem of throttle valve is interconnectedwith sleeve 8-3 by linkage 90 and is moved in the direction to closevalve 23 when the sleeve moves upwardly in response to an increase inturbine speed thereby reducing the speed of the turbine and converselyis moved to open valve in response to a downward movement of sleeve 88resulting from a decrease in turbine speed. Thus the fly ball governoradjusts valve a 28 in a manner to maintain the speed of turbinesubstantially constant.

The load on the power plant, i. e., the load supplied over transmissionlines 84, is measured by watt meter 52 operatively connected with thesetransmission lines.

Eince the load on the power plant determines the posi tion at whichthrottle valve 28 is placed, the greater the load the further this valveis moved to its open position, and since variations in the positioningof throttle valve 23 affect the adjustment of the feeder 36, due to thecontrol of this feeder being responsive to the steam pressure deliveredto the throttle valve, causing the feeder to feed fuel to mill 34) at anincreased rate as the opening of this valve is increased in order tomaintain this pressure constant and finally since the current drawn bymotor 34 is responsive to the rate of feed to mill 39 it will be seenthat the control of the rate of fuel firing through burner 16 and thecontrol of the activation of flame igniter fill is ultimately responsiveto the load on the power plant and that so long as the activation offlame igniter Ell is responsive to a condition reflecting a decrease inthis load to a value above that at which the flame in furnace 12 becomesunstable, which condition is manifest before the flame becomes unstable,the broad aspect of this invention will be realized. It is thus apparentthat several modified forms of control circuits may be used in lieu ofthe particular arrangement of Fig. 1. Fig. 2, 3 and 4 show three suchmodifications.

In the circuit of Fig. 2 conductors 64 and 66 are connected acrosspotential 63. In series with conductor 66 is switch 94 operated by lever42 and arranged to be closed by this lever when it is at a positionrepresenting a predetermined rate of fuel supply to mill 3:; andaccordingly burner to below which rate the flame in furnace 12 becomesunstable with the switch remaining closed for all rates below thispredetermined rate. As pointed out hereinbefore upward or clockwisemovement of lever 42 decreases the rate of feed of feeder 36. Theclosing of switch fi iactivates flame igniter 50 thereby preventing theflame from becoming unstable due to a low rate of fuel firing.

In Fig. 3 the energization of electric circuit 93 is controlled byswitch 96. This switch is connected to and operated by linkage whichforms a part of the governor operating mechanism and interconnects valve28 with the governor. The switch 96 is arranged so that it is closed andflame igniter 56 is energized when valve 28 is moved to a position whichcorresponds with a predetermined fuel flow through burner 16 below whichthe flame in furnace 12 is unstable with the switch remaining closed forall positions of valve 28 corresponding to fuel flows below saidpredetermined flow.

In Fig. 4 energization of the electric circuit is controlled by switch98 having contacts 100 and 102. This switch is operated in accordancewith movements of the indicator of the watt meter 92 and is arranged sothat contacts 100 and 102 are closed and flame igniter St) is energizedwhen the indicator of this meter is in a position which corresponds witha predetermined rate of fuel firing through burner 16 below which theflame in furnace 12 becomes unstable with the contacts remaining inengagement for all positions of this indicator representing a rate offuel firing below this predetermined rate.

It will thus be seen that this invention provides a control for theauxiliary flame igniter which is effective to activate the igniterbefore a dangerous condition arises in the furnace thereby eliminatingthe possibility of an explosion.

While we have illustrated and described a preferred embodiment of ournovel organization it is to be understood that such is merelyillustrative and not restrictive and that variations and modificationsmay be made therein without departing from the spirit and scope of theinvention. We therefore do not wish to be limited to the precise detailsset forth but desire to avail ourselves of such changes as fall withinthe purview of our invention.

What we claim is:

1. A power plant comprising in combination a vapor generator, a primemover generator unit driven by vapor from said vapor enerator, saidvapor generator including a furnace, burn-er means for projecting fuelinto said furnace with said fuel being burned within said furnace, saidburner being operable over a given range of rates of firing, adjustablemeans for controlling said rate of firing of said burner, meanseffectively regulated in accordance with the load on the power plant andoperative to control the last named means in such a manner that theoutput of the power plant reflects the adjustment thereof, said furnacebeing of such a size and said burner being of such a construction and sorelated to the furnace that the flame produced by the burning fuelwithin the furnace is unstable for a given portion of the lower end ofsaid range of operation of the burner, an auxiliary flame igniter thatis of small capacity with relation to said burner and disposed adjacentto said burner and in such relation thereto that when it is activated itis effective to stabilize said unstable flame, and means responsive to acondition manifest prior to the reduction of the rate of fuel supply tothe vapor generator below the value whereat said flame becomes unstableand reflecting a decrease in load on said power plant to a predeterminedvalue for activating said auxiliary flame igniter before said flamebecomes unstable thereby preventing such instability and the ineflicientcombustion and dangerous condition incident thereto.

2. The organization of claim 1 wherein the means that controlsactivation of the auxiliary flame igniter includes electrical meansoperative to directly measure the load on the prime mover generator unitand means responsive to said electrical means for activating saidauxiliary flame igniter when the load decreases to said predeterminedvalue.

3. In combination, a boiler having a furnace fired by pulverized fuelthrough a suitable burner, means for supplying said fuel to said burnerincluding a pulverizer and a fuel feeder operative to regulate the rateof fuel supply to said pulverizer and including adjustable means forvarying said rate, means effectively controlled in accordance with theload on the boiler operative to control said adjustable means toregulate the rate of fuel supply so that the output of the boiler willmeet said load, the burner being operable and the fuel rate beingregulated over a given range of rates of firing, the burner being ofsuch a construction and so related to the furnace that the flameproduced by the burning fuel within the furnace is unstable for a givenportion of the lower end of said range of regulation, an auxiliary flameigniter that is of small capacity with relation to said burner anddisposed adjacent said burner and in such relation thereto that when itis activated it is efiective to stabilize said unstable flame, and meanscontrolled in accordance with the control of said adjustable means andoperative to activate said auxiliary flame igniter immediately prior tothe rate of fuel supply being lowered to the point I where the flamebecomes unstable.

4. In combination, a boiler for generating steam, said boiler having apulverized fuel system including a burner for projecting the pulverizedfuel into the furnace of the boiler with the fuel being burned withinthe furnace, a pulverizer connected to supply said burners withpulverized fuel and a regulatable feeder operative to reg- Cit ulate therate of feed of fuel to the pulverizer, means effectively controlled inaccordance with the load on the boiler and operative to control saidfeeder to regulate the rate of feed so the output of the boiler willmeet the load imposed thereon, the burner being operable and he fuelrate being regulated over a given range of rates of firing, the furnacebeing of such a size and the burner being of such a construction and sorelated to the furnace that the flame produced by the burning fuelwithin the furnace is unstable for a given portion of the lower end ofsaid range of regulation, electric motor means for driving saidpulverizer, the electric current required by said motor means decreasingwith a decrease in the rate of fuel supply, an auxiliary flame igniterthat is of small capacity with relation to said burner and disposedadjacent said burner and in such relation thereto that when it isactivated it is effective to stabilize said unstable flame, and meanseffectively responsive to the amperage drawn by said motor meanseffective to activate said auxiliary flame igniter when said amperagefalls to a predetermined value reflecting a rate of feed at leastsomewhat higher than the rate at which said flame becomes unstable.

5. A power plant comprising a steam generator and a turbine generatorunit driven by steam from said steam generator, said steam generatorincluding a furnace, a. fuel firing system including a main burnerthrough which fuel is projected into said furnace and burnedtherewithin, said burner being operable over a given range of rates offiring, said furnace being of such asize and said burner being of such aconstruction and so related to the furnace that the flame produced bythe burning fuel within the furnace is unstable for a given portion ofthe lower end of said range of operation of the burner, adjustable meansoperative to control the rate of firing of said burner, meanseffectively regulated in accordance with the load on the power plant tocontrol said last named means so as to maintain the steam supplied tothe turbine at a substantially constant pressure, valve means forcontrolling the amount of steam supplied to the turbine, a governorresponsive to the speed of the turbine and operative to regulate saidvalve to maintain the turbine speed substantially constant, an auxiliaryflame igniter that is of small capacity with relation to said mainburner and in such relation thereto that when it is activated it iseffective to stabilize said unstable flame, and means to activate anddeactivate said igniter, said means being responsive to the regulatingaction of the governor and regulated thereby to activate said auxiliaryflame igniter prior to the reduction of the rate of fuel supply to thepoint where the flame becomes unstable.

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